Throw insignificant first three out (5)

I believe the answer is:

fling

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'throw' is the definition.
(I know that fling is a kind of the throw)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for fling that I've seen before include "knees-up at 8 [HIGHLAND GAMES]" , "Try" , "Brief affair - chuck" , "Spell of indulgence" , "Launch or propel" .)

I've seen this clue in The Daily Express.

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